Sheet transport device, sheet transport control method, and printer

ABSTRACT

According to one aspect of the embodiment, a sheet transport device includes a detecting unit configured to detect skew with respect to a transport direction of a sheet that is supplied, a transport unit configured to transport the sheet using a plurality of transport members disposed on the right and on the left at different intervals from an upstream side toward a downstream side in the transport direction and a control unit configured to cause rotation velocities of transport members on the right among the plurality of transport members to be different from rotation velocities of transport members on the left among the plurality of transport members in accordance with the skew of the sheet detected by the detecting unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2011-8233, filed on Jan. 18, 2011, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a transport technique of transporting a taken sheet while monitoring and correcting skew of the sheet.

BACKGROUND

In printers, copiers, and the like for performing printing on a sheet, a sheet is transported while in contact with a rotating rod-shaped transport roller or the like, for example. However, when the sheet is not normally set in a printer or the like, or when the sheet comes into contact with the transport roller in a skewed manner, the sheet is transported without any correction. Furthermore, when printing is performed on a skewed sheet or when data to be copied is read from a skewed sheet, printing or copying is not accurately performed. Thus, in order to perform printing or copying at a proper position or in a proper direction on a sheet taken in a certain printing direction, the position of the sheet is corrected. As examples of a technique for such correction, a technique of causing a sheet to come into contact with a registration roller while transporting the sheet using a transport roller, and a technique of rotating a plurality of transport rollers placed on the right and on the left at different velocities are known.

Regarding techniques of correcting such skew of a sheet, there is suggested a device that includes a spherical motor disposed on the output side of a transport roller and a pressing unit facing the spherical motor, and that drives the spherical motor in accordance with a detected skew or lateral displacement to correct the attitude of a sheet (for example, Japanese Laid-open Patent Publication No. 8-108954). Also, there is suggested a device that measures a time difference of detection of the leading end of a sheet using a plurality of sensors, and that rotates rollers disposed in parallel on the right and on the left on the basis of the measurement result so that the sheet comes into contact with a registration roller (for example, Japanese Laid-open Patent Publication No. 2008-233446).

There is suggested a device that includes a plurality of registration rollers and a plurality of passage detecting sensors disposed at certain intervals in a direction substantially perpendicular to a transport direction, and that performs skew correction by calculating skew of the leading end of a sheet and by controlling the rotation velocities of the registration rollers (for example, Japanese Laid-open Patent Publication No. 2005-306608). Also, there is suggested a device that includes a center transfer roller disposed in a center portion of a transport path and a pair of end transfer rollers the end portion of which overlaps the center transfer roller, and that sets a velocity difference to the pair of end transfer rollers on the right and on the left in accordance with a detected skew (for example, Japanese Laid-open Patent Publication No. 9-244436).

A technique of causing a supplied sheet to come into contact with a registration roller or the like to correct the direction of the sheet is available. However, correction of a large skew has limitations. For example, in order to correct a large skew of a sheet with respect to a registration roller, the sheet is bent considerably. However, extending a sheet transport path by a large amount involves a negative effect and is not practical. Furthermore, a sheet may become wrinkled when coming into contact with the registration roller, or a counteraction at the time of coming into contact may lead to a paper jam in the device. Also, when two contact rollers for transporting a sheet are driven at different rotation velocities on the right and on the left, the two contact rollers apply different loads to a sheet sandwiched there between in accordance with the distance from the center of rotation to the sheet, which is likely to cause wrinkles.

SUMMARY

According to an aspect of the invention, a sheet transport device includes a detecting unit configured to detect skew with respect to a transport direction of a sheet that is supplied, a transport unit configured to transport the sheet using a plurality of transport members disposed on the right and on the left at different intervals from an upstream side toward a downstream side in the transport direction and a control unit configured to cause rotation velocities of transport members on the right among the plurality of transport members to be different from rotation velocities of transport members on the left among the plurality of transport members in accordance with the skew of the sheet detected by the detecting unit.

The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an exemplary functional configuration of a transport device according to a first embodiment.

FIG. 2 is a flowchart illustrating an example of a transport control process.

FIGS. 3A and 3B are diagrams illustrating an example of the state of correcting skew toward the left with respect to a transport direction.

FIG. 4 is a diagram illustrating an example of the state of correcting skew toward the right with respect to the transport direction.

FIG. 5 is a diagram illustrating an exemplary configuration of a printer according to a second embodiment.

FIG. 6 is a diagram illustrating an exemplary configuration of a sheet skew detector.

FIG. 7 is a diagram illustrating an example of a principle of skew detection.

FIG. 8 is a diagram illustrating an example of a principle of skew detection.

FIG. 9 is a diagram illustrating an exemplary configuration of a sheet transporter.

FIG. 10 is a diagram illustrating an exemplary configuration of driving transport members.

FIGS. 11A and 11B are diagrams illustrating an exemplary configuration of the transport members.

FIG. 12 is a diagram illustrating an example of the state of correcting skew.

FIG. 13 is a diagram illustrating an exemplary hardware configuration of the printer.

FIG. 14 is a diagram illustrating an exemplary functional configuration of the printer.

FIG. 15 is a diagram illustrating an example of a rotation velocity setting table.

FIG. 16 is a flowchart illustrating an example of a sheet transport process.

FIG. 17 is a flowchart illustrating the example of the sheet transport process.

FIG. 18 is a flowchart illustrating the example of the sheet transport process.

FIG. 19 is a diagram illustrating an exemplary functional configuration of a transport device according to a third embodiment.

FIG. 20 is a diagram illustrating an exemplary configuration of a printer.

FIG. 21 is a flowchart illustrating an example of a sheet transport process.

FIG. 22 is a flowchart illustrating the example of the sheet transport process.

FIG. 23 is a flowchart illustrating the example of the sheet transport process.

FIG. 24 is a flowchart illustrating the example of the sheet transport process.

FIG. 25 is a diagram illustrating an exemplary configuration of transport members according to another embodiment.

FIG. 26 is a diagram illustrating an example of the state of correcting skew.

FIGS. 27A and 27B are diagrams illustrating a transport device according to a comparative example.

DESCRIPTION OF EMBODIMENTS First Embodiment

A first embodiment will be described with reference to FIGS. 1 to 4. FIG. 1 is a diagram illustrating an exemplary configuration of a transport device 2 according to the first embodiment. The configuration illustrated in FIG. 1 is an example, and is not limited thereto.

The transport device 2 is an example of the sheet transport device disclosed herein, and detects skew of a sheet that is transported, and transports the sheet while correcting the orientation of the sheet to be appropriate with respect to a transport direction. The transport device 2 includes, for example, a sheet skew detector 4, a sheet transporter 6, and a controller 8.

The sheet skew detector 4 is an example of a unit that detects whether or not there is a sheet supplied to the transport device 2, and that detects skew with respect to a transport direction. For example, the sheet skew detector 4 includes a plurality of sensors, detects a sheet placed at a certain position in the transport device 2, also detects skew and orientation of the sheet on the basis of a difference in detection timing between the sensors, and notifies the controller 8 of the detection result.

The sheet transporter 6 is an example of a unit that transports a sheet in a certain direction, and includes, for example, a plurality of transport members 61 to 68. The transport members 61 to 68 are constituted by rollers having a reduced contact area that contacts a sheet, and are disposed on the right and on the left at different intervals from the upstream side toward the downstream side in the transport direction, for example. The transport members 61 to 68 are rotatable in the transport direction independently from one another, and are capable of applying a transport load to a sheet when the surfaces of the rollers come into contact with the sheet, thereby leading the sheet in the transport direction, for example. The transport members 61 to 68 are rotated at the same rotation velocity, and are capable of transporting, in the transport direction, a sheet placed in a normal orientation in the transport device 2, for example. When the sheet skew detector 4 detects skew of the sheet, the rotation velocities of the transport members 61 to 68 on the right and on the left may be varied to correct the skew, for example.

In the sheet transporter 6 illustrated in FIG. 1, the disposition intervals of the transport members 61 to 68 are increased toward the downstream side in the transport direction. Specifically, the interval between the transport members 61 and 62 is represented by X₁, the interval between the transport members 63 and 64 is represented by X₂, the interval between the transport members 65 and 66 is represented by X₃, and the interval between the transport members 67 and 68 is represented by X₄, in which X₄>X₃>X₂>X₁ is satisfied. The transport members 61 to 68 are symmetrically disposed in a V-like shape along a transport path, for example. Accordingly, a sheet that has passed the sheet skew detector 4 comes into contact with the transport members 61 and 62 at the center of the leading end thereof, and receives a transport load, for example. Furthermore, the sheet comes into contact with the other transport members 63 to 68 disposed at larger intervals and receives a transport load as the sheet is transported in the transport direction.

The number of transport members illustrated in FIG. 1 is an example, and may be increased or decreased. Also, the disposition state of the transport members 61 to 68 on the right and on the left is an example. In the sheet transporter 6 illustrated in FIG. 1, two transport members are disposed in each line in a direction perpendicular to the transport direction. Alternatively, three or more transport members may be disposed in each line. Furthermore, the number of transport members may vary in individual lines.

The controller 8 is an example of an operation controller of the transport device 2, and calculates a skew amount of a sheet, controls the operation of the sheet transporter 6, and controls skew correction. For example, the controller 8 recognizes a disposition state of a sheet on the basis of a detection result received from the sheet skew detector 4, calculates a skew amount, and determines a skew orientation. Also, the controller 8 outputs a transport instruction to the sheet transporter 6 on the basis of the determination result. The transport instruction includes, for example, an operation instruction to rotate the transport members 61 to 68 at uniform velocity or to vary the rotation velocities on the right and on the left on the basis of a skew amount. The controller 8 may include, for example, a measuring unit that measures a difference in timing of detecting a sheet by the sheet skew detector 4.

Next, a transport control process will be described with reference to FIG. 2. FIG. 2 is a flowchart illustrating an example of the transport control process. The procedure and details of the process illustrated in FIG. 2 are an example, and are not limited thereto.

The transport control process is an example of the sheet transport control method disclosed herein. The sheet skew detector 4 detects a sheet placed at a certain position of the transport device 2, and notifies the controller 8 of the detection (step S1). Also, the sheet skew detector 4 detects skew of the placed sheet (step S2). In the skew detection, the sheet skew detector 4 detects the sheet that has been transported to the sheet skew detector 4, and a difference in detection timing between the sensors, for example.

Then, the controller 8 receives a detection result generated by the sheet skew detector 4 and calculates a skew amount of the sheet (step S3). In the calculation of the skew amount, the controller 8 calculates the skew amount of the sheet, for example, a skew distance and a skew angle, by using the transport velocity of the sheet, the difference in detection timing of the sheet by the sheet skew detector 4, the rotation velocities of the transport members 61 to 68, and so forth.

The controller 8 controls the transport operation on the basis of the calculated skew amount (step S4). When no skew is detected, the controller 8 causes the transport members 61 to 68 to be rotated at uniform velocity so that the sheet is transported in a direction parallel to the transport direction, for example. When skew is detected, the controller 8 varies the rotation velocities of the transport members 61 to 68 on the right and on the left on the basis of the above-described calculated skew angle and so forth, and causes the sheet to be rotationally transported at a normal angle with respect to the transport direction. In this case, the rotation velocities of the transport members 61 to 68 may be controlled by using, for example, a table in which rotation velocities are set in association with calculated skew angles. Also, in the control of the rotation velocities of the transport members 61 to 68 on the right and on the left, the controller 8 may decrease the rotation velocities of the transport members on the side on which the sheet is detected first by one of the sensors provided in the sheet skew detector 4. Alternatively, the controller 8 may increase the rotation velocities of the transport members on the side on which the sheet is detected later. Alternatively, the controller 8 may perform both the decrease and increase of the rotation velocities.

Next, an example of a skew correction operation will be described with reference to FIGS. 3A, 3B, and 4. FIGS. 3A and 3B are diagrams illustrating an example of the state of correcting skew toward the left with respect to the transport direction. FIG. 4 is a diagram illustrating an example of the state of correcting skew toward the right with respect to the transport direction. The configurations illustrated in FIGS. 3A, 3B, and 4 are an example, and are not limited thereto.

Referring to FIG. 3A, a sheet 10 is placed on the sheet transporter 6 while being skewed toward the right with respect to the transport direction. In this case, the controller 8 (FIG. 1) recognizes that the left side of the sheet 10 is being transported faster with respect to the transport direction, on the basis of a detection result received from the sheet skew detector 4 (FIG. 1). Thus, the controller 8 decreases the rotation velocities of the transport members on the side on which the sheet 10 is detected first, or increases the rotation velocities of the transport members on the side on which the sheet 10 is detected later. Specifically, the controller 8 controls the sheet transporter 6 to cause the rotation velocities of the transport members 61, 63, 65, and 67 on the right with respect to the transport direction to be higher than the rotation velocities of the transport members 62, 64, 66, and 68 on the left. In this case, for example, the rotation velocities of the transport members 61, 63, 65, and 67 on the right are set to be the same, and the rotation velocities of the transport members 62, 64, 66, and 68 on the left are set to be the same.

Accordingly, a difference in rotation velocity is generated between the right and left sides in the sheet transporter 6, so that the skew of the sheet 10 may be corrected toward the left with respect to the transport direction with the sheet 10 being transported in the transport direction, as illustrated in FIG. 3B. Here, the rotation velocities set to the transport members 61 to 68 on the right and on the left, and the time period over which the rotation velocities are varied may be determined on the basis of a skew angle, a skew amount, etc. calculated from the detection result generated by the sheet skew detector 4. Alternatively, the rotation velocities and the time period may be arbitrarily set by a user.

FIG. 4 illustrates a case where the sheet 10 is skewed toward the left with respect to the transport direction, that is, a case where the sheet skew detector 4 detects the right side of the sheet 10 first. In this case, the controller 8 causes the rotation velocities of the transport members 62, 64, 66, and 68 on the left with respect to the transport direction to be higher than the rotation velocities of the transport members 61, 63, 65, and 67 on the right. Accordingly, the skew may be corrected toward the right while transporting the sheet 10 in the transport direction.

According to the above-described configuration, the disposition intervals of the plurality of transport members on the right and on the left are varied, so that the transport load applied to a sheet is distributed and the occurrence of wrinkling may be suppressed in the case of correcting skew while transporting the sheet. Also, the plurality of rollers are disposed at different intervals from the upstream side toward the downstream side in the transport direction, so as to set a wide skew correction section. Accordingly, the rotation velocity of each transport member may be suppressed, skew correction may be appropriately performed, and the occurrence of wrinkling may be suppressed. Furthermore, since the transport members disposed at different intervals have a small contact area, the contact load applied to the sheet may be suppressed.

Second Embodiment

A second embodiment will be described with reference to FIGS. 5 to 18.

FIG. 5 is a diagram illustrating an exemplary configuration of a printer 20 according to the second embodiment. The configuration illustrated in FIG. 5 is an example, and is not limited thereto.

The printer 20 is an example of the printer disclosed herein, and includes a print operation unit 22, lower casing units 24 and 26, and a transport mechanism for detecting skew of a sheet 10 on which a printing process is performed and transporting the sheet 10 while correcting the skew, as illustrated in FIG. 5. The print operation unit 22 is a function unit that prints characters and images on the sheet 10, and includes transport rollers 28 and 30, a processing unit 32, a fixing unit 34, an output unit 36, a controller unit 38, and a mechanism control unit 40, for example. The lower casing unit 24 is a function unit that supplies the sheet 10, and includes a sheet cassette 42, a sheet skew detector 44, and a sheet transporter 46, for example. The sheet skew detector 44 and the sheet transporter 46 correspond to the sheet skew detector 4 and the sheet transporter 6 of the transport device 2, respectively. The lower casing unit 26 includes a sheet cassette 48, for example.

The transport rollers 28 and 30 are an example of a unit that receives the sheet 10 supplied from the lower casing unit 24 to the print operation unit 22 and transports the sheet 10 to a print path 50. The transport rollers 28 and 30 sandwich the front and rear sides of the sheet 10 and guide the sheet 10 to the processing unit 32, for example.

The processing unit 32 is an example of an image transfer function unit that transfers characters and images onto the sheet 10. For example, the processing unit 32 generates an image to be printed from image data or the like received by the controller unit 38 from an external computer 52 connected to the printer 20, and transfers the generated image onto the sheet 10. The processing unit 32 includes, for example, a drum 54 that generates an electrostatic latent image from image data, and a transfer roller 56 that electrically transfers a toner image, which is generated on the drum 54 from toner serving as an example of a coloring material, onto the sheet 10.

The fixing unit 34 is an example of a fixing unit that fixes a toner image onto the sheet 10, and includes, for example, a heating roller 58 and a pressure roller 70. The heating roller 58 heats the toner image. The pressure roller 70 presses the heated toner image onto the sheet 10, so as to fix the toner image onto the sheet 10. The sheet 10 with the toner image fixed there onto is output through the output unit 36 to the outside of the printer 20.

The controller unit 38 is an example of a control function unit that transmits and receives an operation control instruction and state information to and from a print function including the processing unit 32 and the fixing unit 34, and the mechanism control unit 40, and constitutes the controller 8 of the above-described transport device 2 (FIG. 1). The controller unit 38 receives a print instruction and print data from the external computer 52 serving as an external apparatus, and controls printing, for example.

The mechanism control unit 40 is an example of a mechanism control unit that is controlled by the controller unit 38 and executes mechanism operation control of the processing unit 32, the fixing unit 34, the sheet skew detector 44, the sheet transporter 46, and so forth, and constitutes the controller 8 of the transport device 2 (FIG. 1). The mechanism control unit 40 includes therein, for example, a sheet skew calculator 72, which calculates a skew amount and a skew angle of the sheet 10 on the basis of a detection result supplied from the sheet skew detector 44, and which outputs an operation control instruction based on the calculation result to the sheet transporter 46.

The sheet skew detector 44 is an example of a sheet skew detecting unit that monitors whether the sheet 10 taken from the sheet cassette 42 or 48 serving as a sheet feeder is being transported in a certain orientation and direction along a transport path 74 in the lower casing unit 24. The sheet skew detector 44 detects a skew amount of the sheet 10 transported thereto, information about a transport time, etc. by using a noncontact sensor or the like, and notifies the sheet skew calculator 72 of the mechanism control unit 40 of the detection result, for example.

The sheet transporter 46 is an example of a transport unit that transports the sheet 10 to transport rollers 76 and 78 while correcting skew of the sheet 10 in response to an instruction provided from the mechanism control unit 40. The sheet transporter 46 includes, for example, the transport members 61 to 68 that are to be in contact with the rear side of the sheet 10 and transport members 601 to 608 that are to be in contact with the front side of the sheet 10, which serve as a configuration enabling the sheet 10 to be rotated to the right or to the left with respect to the transport direction. The sheet 10 on which skew correction has been performed by the sheet transporter 46 is taken by the transport rollers 76 and 78 and is led to the print operation unit 22.

The sheet cassettes 42 and 48 are an example of a unit that stores sheets 10 serving as printing media and holds the sheets 10 at certain positions. A sheet feeding unit 80 that feeds the sheet 10 stored in the sheet cassette 42 to the transport path 74 is provided in the lower casing unit 24. Also, a sheet feeding unit 82 that feeds the sheet 10 stored in the sheet cassette 48 to the transport path 74 is provided in the lower casing unit 26.

Next, sheet skew detection will be described with reference to FIGS. 6 to 8. FIG. 6 is a diagram illustrating an exemplary configuration of the sheet skew detector 44, FIG. 7 is a diagram illustrating an example of a principle of skew detection, and FIG. 8 is a diagram illustrating an example of a principle of skew detection. The configuration, detection state, and detection procedure illustrated in FIGS. 6 to 8 are an example, and are not limited thereto.

The sheet skew detector 44 illustrated in FIG. 6 includes an optical sensor 90 that detects, in a noncontact manner, the sheet 10 transported along the transport path 74 (FIG. 5), for example. The optical sensor 90 includes, for example, a light emitting unit 92 and a light receiving unit 94, and has measurement points A and B (FIG. 7) arranged in the direction perpendicular to the transport direction. The light emitting unit 92 faces the front side of the sheet 10. The light receiving unit 94 faces the rear side of the sheet 10. The optical sensor 90 determines that there is the sheet 10 by detecting cutting off of light emitted from the light emitting unit 92 when the sheet 10 is transported.

The measurement points A and B in the optical sensor 90 are set at an interval L on a straight line extending along the direction perpendicular to the transport direction, for example. In the process of transporting the sheet 10 illustrated in FIG. 7, for example, the sheet 10 is transported such that the leading end of the sheet 10 is perpendicular to the transport direction, and no skew occurs. In this case, the light receiving unit 94 of the optical sensor 90 simultaneously detects cutting off of light at the measurement points A and B. That is, a time difference t in detection timing between the measurement points A and B is zero, so that a skew amount N is determined to be zero.

In the sheet skew detector 44 illustrated in FIG. 8, for example, cutting off of light is detected at the measurement point A first, and then cutting off of light is detected at the measurement point B after a certain time period t has elapsed. The certain time period t, which is a time difference in detection timing of cutting off of light, corresponds to the time period from when the leading end of the sheet 10 is detected at the measurement point A to when the leading end of the sheet 10 is detected at the measurement point B. In this way, light is cut off at the measurement point A first, and light is cut off at the measurement point B later. Thus, the sheet 10 is skewed toward the right with respect to the transport direction, and the left side thereof is transported faster.

When skew is detected, a skew amount N is calculated to obtain a skew correction angle θ for correcting the skew. Here, the skew amount N indicates the distance by which the sheet 10 is transported during the time difference in detection timing of cutting off of light. Thus, the skew amount N (mm) is calculated on the basis of transport velocity V (mm/sec) and time difference t (sec).

N (mm)=V (mm/sec)×t (sec)  (1)

The skew correction angle θ is calculated on the basis of the skew amount N and a disposition interval L of the measurement points. For example, the following expression may be satisfied when using a trigonometric function.

Skew correction angle θ=tan⁻¹(N/L)  (2)

Here, a description has been given of a detection process performed when the sheet 10 is skewed toward the right. A process similar to this process may be performed when the sheet 10 is skewed toward the left.

Next, the configuration of the sheet transporter 46 will be described with reference to FIGS. 9 to 12. FIG. 9 is a diagram illustrating an exemplary configuration of the sheet transporter 46, FIG. 10 is a diagram illustrating an exemplary configuration of driving the transport members 61 to 68 and 601 to 608, FIGS. 11A and 11B are diagrams illustrating an exemplary configuration of the transport members 61 to 68 and 601 to 608, and FIG. 12 is a diagram illustrating an example of the state of correcting skew. The configurations illustrated in FIGS. 9 to 12 are an example, and are not limited thereto.

The sheet transporter 46 illustrated in FIG. 9 is an example of a transport unit, and includes, for example, the transport members 61 to 68 for the rear side of the sheet 10, which are disposed on the right and on the left at different intervals from the upstream side toward the downstream side in the transport direction, and the transport members 601 to 608 for the front side of the sheet 10, which are disposed at the positions facing the transport members 61 to 68, respectively. The transport members 61 to 68 and 601 to 608 are constituted by spherical roller members having a small contact area for the sheet 10, and are disposed in a V-like shape at disposition intervals X₁ to X₄, which are increased from the upstream side toward the downstream side.

The individual transport members 61 to 68 and 601 to 608 are configured to be independently rotatable, the rotation velocities thereof being increased or decreased in accordance with a detected skew amount, and are capable of correcting the orientation of a transported sheet 10 using balanced rotation velocities, for example.

The transport members 61 to 68 and 601 to 608 illustrated in FIG. 10 face each other with the front and rear sides of the transported sheet 10 disposed therebetween. Each of the transport members 61 to 68 and 601 to 608 may include, for example, a driving motor 100, a clutch gearshift 102, and a belt 104 which serve as a driving unit.

The driving motor 100 is an example of a power generating unit for rotating a corresponding one of the transport members 61 to 68 and 601 to 608, and may perform, for example, driving, stopping, acceleration, and slowdown, in accordance with an operation instruction provided from the mechanism control unit 40.

The clutch gearshift 102 is an example of a unit that maintains the rotation power of the driving motor 100 at a certain rotation velocity or that adjusts and transmits the rotation power. In a process of correcting skew of the sheet 10, the rotation velocities of the individual transport members 61 to 68 and 601 to 608 may be controlled by controlling the rotation velocity of the clutch gearshift 102. In the case of enabling adjustment of rotation velocities on the driving motor 100 side, for example, the clutch gearshift 102 may be omitted.

The belt 104 is an example of a unit that transmits the rotation power obtained from the driving motor 100 to a corresponding one of the transport members 61 to 68 and 601 to 608. The function of shifting the power obtained from the driving motor 100 may be realized by a combination of the clutch gearshift 102 and the belt 104.

Alternatively, a single driving motor 100, a single clutch gearshift 102, and a single belt 104 may be shared by a plurality of the transport members 61 to 68 and 601 to 608.

Each of the transport members 61 to 68 and 601 to 608 includes, for example, a spherical roller 110, fixing frames 112 and 114, and a plurality of guide rollers 116, as illustrated in FIG. 11A. The fixing frames 112 and 114 fix the spherical roller 110 from the upper and lower sides thereof such that a portion of the spherical roller 110 to be in contact with the sheet 10 is exposed. On the inner side of the fixing frames 112 and 114, the guide rollers 116 are disposed to be in contact with the spherical roller 110. The guide rollers 116 may have a bearing function for fixing the spherical roller 110 while reducing the contact resistance between the fixing frames 112 and 114 and the spherical roller 110.

FIG. 11B is a diagram viewed from the side on which the spherical roller 110 contacts the sheet 10. The fixing frame 114 has a hole 118 for causing part of the spherical roller 110 to be exposed, for example. On the inner side of the fixing frame 114, the guide rollers 116 are disposed around the hole 118 so as to be in contact with the spherical roller 110. Accordingly, in each of the transport members 61 to 68 and 601 to 608, only a contact point of the exposed spherical roller 110 may come into contact with the sheet 10. Also, the guide rollers 116 disposed on the inner side of the fixing frames 112 and 114 cause the spherical roller 110 not to be moved. Accordingly, for example, the spherical roller 110 does not receive frictional resistance caused by contact with the fixing frames 112 and 114, so that the rotation power applied to the spherical roller 110 may be efficiently transmitted to the sheet 10.

The sheet transporter 46 including the above-described transport members 61 to 68 and 601 to 608 corrects skew of the sheet 10 by varying the rotation velocities of the transport members 61 to 68 and 601 to 608 on the right and on the left, as illustrated in FIG. 12. In the skew correction, for example, the rotation velocities of the transport members on the side on which the sheet 10 is detected first by the sheet skew detector 44 may be decreased, or the rotation velocities of the transport members on the side on which the sheet 10 is detected later may be increased, as described above. Alternatively, both the decrease and increase of the rotation velocities may be performed. In other words, the relative rotation velocities are varied on the right and on the left.

In the case of correcting skew, the transport operations of the individual transport members 61 to 68 and 601 to 608 are performed so that all the transport members on the right operate simultaneously and all the transport members on the left operate simultaneously. For example, as illustrated in FIG. 12, the rotation velocities of the transport members 61, 63, 65, and 67 on the right with respect to the transport direction are uniformly increased. Likewise, the rotation velocities of the transport members 62, 64, 66, and 68 on the left are uniformly decreased. In this case, the difference in the relative rotation velocities set to the transport members on the right and on the left is minimized. Also, since the transport members 61 to 68 and 601 to 608 are disposed in a V-like shape, the transport force applied to the sheet 10 transported by the sheet transporter 46 gradually increases from the center of the leading end of the sheet 10 toward the right and left. Accordingly, the transport force on the right and on the left applied to the sheet 10 is minimized, which suppresses the occurrence of wrinkling of the sheet 10. Also, the angle of the sheet 10 is not rapidly changed, and thus errors caused by correcting skew may be suppressed.

Next, an exemplary configuration of the printer 20 will be described with reference to FIGS. 13 to 15. FIG. 13 is a diagram illustrating an exemplary hardware configuration of the printer 20, FIG. 14 is a diagram illustrating an exemplary functional configuration of the printer 20, and FIG. 15 is a diagram illustrating an example of a rotation velocity setting table. The configurations illustrated in FIGS. 13 to 15 are an example, and are not limited thereto.

The printer 20 includes, for example, the controller unit 38, the mechanism control unit 40, the sheet skew detector 44, an operation panel unit 144, and a power supply unit 146. The controller unit 38 includes, for example, a central processing unit (CPU) 130, a data transmitting/receiving unit 132, a storage unit 134, a random access memory (RAM) 142, and a timer 143. The CPU 130 is an example of a processing unit, and executes processing in accordance with a processing program stored in the storage unit 134, thereby controlling the operations of the transport device 2 and the printer 20, for example.

The data transmitting/receiving unit 132 is an example of a communication unit that communicates with the external computer 52 or the like, and is connected to the external computer 52 in a wired or wireless manner, for example. Accordingly, data to be printed may be transmitted and received between the controller unit 38 and the external computer 52. The external computer 52 connected to the data transmitting/receiving unit 132 may be a personal computer (PC) that transmits and receives a print instruction or data to be printed, an apparatus connected to an external communication network, or the like. Alternatively, the external computer 52 may be connected to a database or the like that stores an operation control program or transport control program for the printer 20, or print information and the like.

The storage unit 134 is an example of a storage unit that stores data and programs used in the printer 20, and includes, for example, a program storage unit 136 and a data storage unit 138. The storage unit 134 may be constituted by a read only memory (ROM) or the like. The program storage unit 136 is an example of a unit that stores operation control programs for the printer 20 and the transport device 2, and may store, for example, a print control program, a transport control program, a skew amount calculation program, and a skew correction program. The data storage unit 138 is an example of a unit that stores data used for a printing process, and may store, for example, print data received from the external computer 52, and the rotation velocity setting table 140 used for correcting skew of the transported sheet 10.

The program storage unit 136 and the data storage unit 138 may be constituted by, for example, an electrically erasable and programmable read only memory (EEPROM), the content of which can be electrically rewritten.

The print control program, the transport control program, the rotation velocity setting table 140, and so forth are not limited to those stored in the program storage unit 136 and the data storage unit 138. For example, a program or a table stored in a computer-readable recording medium, such as a magnetic disk, a flexible disk, an optical disc, or a magneto-optical disc, may be used. Furthermore, a program or a table may be read from a server or a database on a network and may be used.

The RAM 142 serves as a working area for executing the print control program, the transport control program, and so forth stored in the storage unit 134, for example. When the CPU 130 executes processing in accordance with these control programs, a transport process and a printing process are executed.

The timer 143 is an example of a unit that measures an elapsed time. For example, the timer 143 detects an elapsed time, which is a difference in detection timing of a skewed sheet 10 between the measurement points A and B set in the optical sensor 90 provided in the sheet skew detector 44.

The mechanism control unit 40 is connected to the controller unit 38 and the sheet skew detector 44, is supplied with power from the power supply unit 146, and controls the operations of the function units of the transport device 2 and the printer 20. As illustrated in FIG. 14, the mechanism control unit 40 receives a control instruction from the controller unit 38, and outputs a skew correction instruction to the driving motor 100 of the sheet transporter 46 on the basis of a calculation result generated by the sheet skew calculator 72. Also, the mechanism control unit 40 outputs a print control instruction to the processing unit 32, the fixing unit 34, the sheet feeding units 80 and 82, and so forth.

The sheet skew detector 44 transmits detection information, such as information about the presence/absence of the sheet 10 detected by the sensor, and information about a time difference in detection timing, to the mechanism control unit 40.

The operation panel unit 144 is constituted by a liquid crystal display (LCD) or the like, and displays control information under control performed by the controller unit 38.

The power supply unit 146 is a unit that is controlled by the controller unit 38, and that supplies power to the function units, such as the driving motor 100 and the processing unit 32, via the mechanism control unit 40.

In a skew correction process performed in the transport device 2, the rotation velocity of the driving motor 100 may be determined in accordance with a calculated skew correction angle θ using the rotation velocity setting table 140 illustrated in FIG. 15, for example. In the rotation velocity setting table 140, the transport members on one of the right and left sides among the transport members 61 to 68 are grouped into group A, and the transport members on the other side are grouped into group B. A value 162 of the velocity of the rollers in group A and a value 164 of the velocity of the rollers in group B may be determined in accordance with a value 160 of a calculated skew correction angle θ. The differences between the velocities of the rollers in group A and the velocities of the rollers in group B set in the rotation velocity setting table 140 are minimized in which skew of the sheet 10 may be corrected by rotationally moving the sheet 10 until the sheet 10 passes the sheet transporter 46. In other words, the differences in relative velocity may be set in view of the length of a transport load section extending from the transport members 61 and 62 on the upstream side to the transport members 67 and 68 on the downstream side in the sheet transporter 46, and the time period over which the sheet 10 passes therethrough, in order to minimize the transport load applied to the sheet 10 to correct skew.

Next, a sheet transport process will be described with reference to FIGS. 16 to 18. FIGS. 16 to 18 are flowcharts illustrating an example of the sheet transport process. The procedure and details of the process illustrated in FIGS. 16 to 18 are an example, and are not limited thereto. In the flowcharts, characters a to c represent links of the flowcharts.

The sheet transport process is an example of the sheet transport control method disclosed herein. In this process, skew of a transported sheet 10 is detected, a skew amount and a correction angle are calculated, the rotation velocities on the right and on the left in the sheet transporter 46 are adjusted to correct the skew of the sheet 10, and the sheet 10 is transported to the print operation unit 22.

Sheet skew detection is started in accordance with the start of feeding of the sheet 10. The start timing may be determined, for example, in response to a print start instruction provided from the external computer 52 or the like, and the optical sensor 90 including the right emitting unit 92 and the right receiving unit 94 of the sheet skew detector 44 is activated. In accordance with the start of printing, it is determined, as initialization of the optical sensor 90, whether or not light is normally being received from the light emitting unit 92 (step S11). For example, when light is not being received by the light receiving unit 94 (NO in step S11), it is determined that the transport device 2 has failure, an error message is displayed, and printing is stopped (step S12).

When light is normally being received (YES in step S11), capturing of the sheet 10 is started. Then, the sheet 10 is transported until light is cut off at both or either of the measurement points A and B in the light receiving unit 94 of the optical sensor 90 and it is detected that the sheet 10 has reached the sheet skew detector 44 (step S13). When the sheet 10 has been detected (YES in step S13), it is determined whether or not the detection timings at the measurement points A and B are the same (step S14). When it is determined that the detection timings at the measurement points A and B are the same (YES in step S14), all the spherical rollers 110 provided in the sheet transporter 46 are rotated at uniform velocity (step S15). In this case, no skew occurs in the captured sheet 10, and thus the sheet 10 is transported without skew correction performed thereon.

When the detection timings at the measurement points A and B are not the same (NO in step S14), it is determined that the captured sheet 10 is skewed, and the orientation of the skew is determined. For example, it is determined whether or not it is at the measurement point A that the sheet 10 has been detected (step S16). The measurement point A is set on the left with respect to the transport direction, as illustrated in FIG. 7. Thus, when the sheet 10 is detected first at the measurement point A (YES in step S16), it is determined that the sheet 10 is skewed toward the right, as illustrated in FIG. 8. Then, the process waits until the sheet 10 is detected at the measurement point B (NO in step S17), and an elapsed time (detection time), which is a difference in detection timing, is measured by the timer 143 (step S18).

When it is determined that the sheet has been detected at the measurement point B (YES in step S17), a skew amount N (distance) and a skew correction angle θ are calculated, and the rotation velocities of the transport members on the right and on the left are adjusted (step S19). In this calculation process, the above equations (1) and (2) (also see FIG. 8) may be used, for example. Then, with reference to the rotation velocity setting table 140, the rotation velocities in groups A and B of the sheet transporter 46 are varied in accordance with the calculated skew correction angle θ. In this case, the velocity in group A may be decreased or the velocity in group B may be increased, or both the decrease and increase may be performed.

After the sheet 10 has been transported to the print operation unit 22, which is a transport destination, it is determined whether or not there is a next sheet 10 (step S20). When there is no next sheet 10, the operation of the transport device 2 is ended. When there is a next sheet 10 and a print instruction (YES in step S20), the process is repeated from step S13.

When it is not at the measurement point A that the sheet 10 has been detected (NO in step S16), it is determined that the sheet 10 is skewed toward the left. In this case, the process for the measurement points A and B may be performed in a reversed manner. That is, an elapsed time, which is a difference in detection timing, until the sheet 10 is detected at the measurement point A is measured (NO in step S21, and then step S22). Then, a calculation process may be performed on the basis of the measured time. Steps S23 and S24 may be performed in a manner similar to steps S19 and S20.

According to the above-described configuration, the disposition intervals of the plurality of transport members on the right and on the left are varied, so that the transport load applied to a sheet is distributed and the occurrence of wrinkling may be suppressed in the case of correcting skew while transporting the sheet. Also, the plurality of rollers are disposed at different intervals from the upstream side toward the downstream side in the transport direction, so as to set a wide skew correction section. Accordingly, the rotation velocity of each transport member may be suppressed, skew correction may be appropriately performed, and the occurrence of wrinkling may be suppressed. Furthermore, since the transport members disposed at different intervals have a small contact area, the contact load applied to the sheet may be suppressed. Also, a printing process may be performed at a proper position by correcting skew of the sheet in a proper orientation.

Advantages and features of first and second embodiments

(1) In the sheet transport device, sheet transport control method, and printer, skew of a transported sheet is calculated by detecting a light source, and the plurality of spherical rollers that are independent from one another and disposed in a V-like shape are individually controlled, thereby skew of the sheet is corrected. The mechanism control unit, which controls driving of the spherical rollers for transporting a sheet, calculates a skew correction angle on the basis of sheet position information supplied from the sheet skew detector, and provides an instruction about the rotation velocities that are desirable for the spherical rollers of the sheet transporter. Accordingly, the amount of skew that may be corrected increases, compared to a configuration according to the related art in which a sheet is caused to come into contact with a stopped registration roller. Also, the occurrence of wrinkling may be reduced compared to a configuration in which two pairs of rod-shaped rollers are driven at different velocities on the right and on the left.

(2) The sheet skew detector detects skew of a sheet on the basis of a time difference in detection at two measurement points.

(3) The sheet skew detector includes the light emitting unit and the light receiving unit. Light is cut off when a sheet passes the light emitting unit and the light receiving unit, and the sheet skew detector detects the position of an end of the sheet.

(4) The sheet transporter includes the plurality of spherical rollers disposed in a V-like shape. When no skew occurs, the sheet is transported without correction performed thereon at the uniform velocity of the spherical rollers in both groups A and B. When skew occurs, the velocities of the spherical rollers are varied in accordance with the orientation of the skew, thereby correcting the skew.

(5) In the sheet transport device, sheet transport control method, and printer, the print quality may be increased, and the skew occurrence rate of a product may be reduced to almost zero.

(6) According to the embodiments, accurate skew correction may be performed regardless of a skew amount, the occurrence of wrinkling may be suppressed by minimizing the load applied to a sheet caused by skew correction, and the print quality may be enhanced. The embodiments may be applied to apparatuses that transport a sheet, such as laser printers, dot impact printers, copiers, and facsimile machines.

Third Embodiment

A third embodiment will be described with reference to FIGS. 19 to 24.

FIG. 19 is a diagram illustrating an exemplary functional configuration of a transport device 200 according to the third embodiment, and FIG. 20 is a diagram illustrating an exemplary configuration of a printer 210. In FIGS. 19 and 20, the same parts as those in FIGS. 1 and 5 are denoted by the same reference numerals, and the corresponding description will be omitted.

The transport device 200 is an example of the sheet transport device disclosed herein, includes the sheet skew detector 4 that detects skew of a captured sheet 10, the sheet transporter 6, and the controller 8, and further includes a second sheet skew detector 202 to which the sheet 10 is transported from the sheet transporter 6. The sheet skew detector 202 is an example of a skew monitoring unit that monitors the sheet 10 transported from the sheet transporter 6 after skew correction has been performed therein. The sheet skew detector 202 is connected to the controller 8, and performs a skew detection process on the sheet 10 transported thereto. When skew is detected in the skew detection process, the sheet skew detector 202 outputs the detection result to the controller 8. The controller 8 receives the detection result, and instructs the sheet transporter 6 to perform re-transport.

In response to the instruction, the sheet transporter 6 rotates the transport members 61 to 68 in the reverse direction so that the sheet 10 is returned to the upstream side in the transport direction, and performs skew correction again.

The printer 210 illustrated in FIG. 20 may be configured as such a re-transport function. The printer 210 is an example of the printer disclosed herein, and includes the transport device 200 having the re-transport function. The transport device 200 includes, for example, a second sheet skew detector 212 to which the sheet 10 is transported from the sheet transporter 46. The sheet skew detector 212 is connected to the sheet skew calculator 72 of the mechanism control unit 40, and monitors the sheet 10 on which skew correction has been performed. When the sheet 10 is still skewed or when the skew amount exceeds an allowable amount, a re-transport process is performed.

The configuration of the sheet skew detector 212 and the skew detection process performed thereby may be similar to those of the above-described sheet skew detector 44, and the description thereof is omitted.

Next, a sheet transport process including a re-transport process will be described with reference to FIGS. 21 to 24. FIGS. 21 to 24 are flowcharts illustrating an example of the sheet transport process. The details and procedure of the process illustrated in FIGS. 21 to 24 are an example, and are not limited thereto. In the flowcharts, characters d to g represent links of the flowcharts.

The sheet transport process is an example of the sheet transport control method disclosed herein. The operations of the sheet skew detector 44 and the sheet skew detector 212 are started in synchronization with feeding of the sheet 10. As described above, the operations of the light emitting unit 92 and the light receiving unit 94 of the optical sensor 90 are started. When the light emitted from the light emitting unit 92 of the sheet skew detector 44 or the sheet skew detector 212 is not normally being received (NO in step S41 or NO in step S43), an error message is displayed, and the operation of the printer 210 is ended (step S42 or S44).

When the light emitted from the light emitting units 92 of the sheet skew detector 44 and the sheet skew detector 212 is normally being received (YES in step S41 and YES in step S43), a transport process is started. The process of detecting skew of the sheet 10, calculating a skew amount and a skew correction angle, and controlling the rotation velocities in the sheet transporter 46 (steps S45 to S51 and steps S55 to S57) may be performed similarly to the above-described steps S13 to S19 and steps S21 to S23 (see FIGS. 16 to 18).

Subsequently, when the sheet skew detector 212 detects the transported sheet 10 at the measurement points A and B (YES in step S52) in the monitoring process for correcting skew, it is determined whether or not the detection timings at the measurement points A and B are the same (step S53). When the detection timings are the same (YES in step S53), or when the difference between the detection timings is within a certain allowable range, it is determined that appropriate skew correction has been performed, the sheet 10 is transported to the print operation unit 22, and it is determined whether or not there is a next sheet 10 (step S54). When there is a next sheet 10 for printing and a print instruction (YES in step S54), the process is repeated from step S45. When there is no next sheet 10 (NO in step S54), the transport process ends.

When the detection timings at the measurement points A and B are not the same (NO in step S53), it is determined that appropriated skew correction has not been performed. Thus, the spherical rollers 110 are rotated in the reverse direction to return the sheet 10 to the sheet transporter 46 (step S61), and the process is repeated from step S45.

The monitoring process for skew correction (steps S58 to S60) may be performed similarly to steps S52 to S54.

According to the above-described configuration, a skew detection process is performed again on a sheet on which skew correction has been performed. When appropriate skew correction has not been performed, a transport process is performed again. Accordingly, the transport process may be appropriately performed, and the print accuracy may be increased.

(1) According to the above-described embodiments, the printers 20 and 210 are described as apparatuses having the transport device 2. Such apparatuses are not limited to these printers, and the transport device 2 may be applied to any other apparatuses that capture a sheet 10 and transport it to a certain position in an appropriate orientation, such as copiers and facsimile machines.

(2) In the above-described embodiments, the rotation velocity setting table 140 that is based on calculated angles is used for setting a difference in velocity among the transport members 61 to 68. The manner of setting the difference is not limited thereto. For example, the rotation velocities of the spherical rollers 110 may be set on the basis of a detected skew amount, a transport distance in a skew correction section, a time period over which the transport members 61 to 68 are operated at different velocities, and so forth.

(3) In the above-described embodiments, differences in rotation velocity are set in the rotation velocity setting table 140 in view of a distance over which a transport load is applied. Alternatively, a certain velocity difference may be set, and an operation period may be controlled in accordance with a calculated skew amount. The rotation period may be varied in accordance with, for example, the size, thickness, or material of the sheet 10.

(4) In the above-described embodiments, each of the transport members 61 to 68 of the transport device 2 or the sheet transporter 46 has a single spherical roller 110 that is to be in contact with the sheet 10. The configuration of the transport members 61 to 68 is not limited thereto. For example, in the transport members 61 to 68 illustrated in FIG. 25, a plurality of transport rollers 220 and 222 may be coupled by a belt 224. Also, as illustrated in FIG. 26, two belts 224 for groups on the right and on the left may be provided, which come into contact with the sheet 10. For example, the sheet transporter 46 includes a belt 224A for constituting the transport members 62, 64, 66, and 68 in group A on the left with respect to the transport direction, and a belt 224B for constituting the transport members 61, 63, 65, and 67 in group B on the right with respect to the transport direction. Also, the transport members 602, 604, 606, and 608 and the transport members 601, 603, 605, and 607 are disposed in a V-like shape with respect to the belts 224A and 224B, respectively, via the sheet 10. With this configuration, the contact area may be increased with respect to the transport direction, whereas the contract area may be decreased with respect to the direction perpendicular to the transport direction. By using the transport members 601 to 608 and the belts 224A and 224B on the right and on the left, a transport force in the transport direction may be increased. Furthermore, even when the rotation velocities are varied for skew correction, the load applied to the sheet 10 in the direction perpendicular to the transport direction may be decreased, so that the occurrence of wrinkling is suppressed.

(5) In the above-described embodiments, detection for determining whether or not a supplied sheet 10 exists and calculating a skew correction angle is performed at the leading end of the sheet 10 in the transport direction, but the manner of detection is not limited thereto. For example, detection may be performed at the trailing end of the sheet 10 that moves in the transport direction. Alternatively, detection may be performed using one or both of side edges of the sheet 10 with respect to the transport direction. That is, detection may be performed at any position as long as the existence of the sheet 10 and a skew angle thereof may be detected.

Next, a comparative example of a transport device according to the related art will be described with reference to FIGS. 27A and 27B. FIGS. 27A and 27B are diagrams illustrating a transport device 300 according to a comparative example.

The transport device 300 illustrated in FIGS. 27A and 27B transports a sheet 10 such that long rod-shaped transport rollers 302 and 304, which extend in the direction perpendicular to the transport direction, are in contact with the sheet 10. The transport rollers 302 and 304 are rotated in the transport direction at uniform velocity, thereby applying a transport load to the sheet 10 to transport the sheet 10. When the rotation velocities of the transport rollers 302 and 304 are difference from each other, different transport loads are applied to the sheet 10, thereby causing the sheet 10 to be wrinkled or damaged. Thus, it is difficult to adjust the rotation velocities during transport.

The rotation direction and rotation velocity of the transport rollers 302 and 304 are uniform. Thus, when the sheet 10 is normally placed as illustrated in FIG. 27A, the sheet 10 may be appropriately transported, and printing may be appropriately performed by a printer or the like. On the other hand, FIG. 27B illustrates a case where the sheet 10 is captured into the transport device 300 in a skewed manner. In this case, the skew is not corrected in the transport device 300, and the sheet 10 is transported without correction. Accordingly, a printing process is performed on the skewed sheet 10. Also, for example, a paper jam may occur or a print head may be damaged in the printer.

In order to overcome such problems, it is desired to provide a configuration for correcting skew in the transport device 300. For example, when a skew correction mechanism is provided before or after the transport device 300, the size of the transport device 300 or the printer increases. In a configuration in which a registration roller or the like that the sheet 10 comes into contact is used as the skew correction mechanism, the amount of skew to be corrected is limited, and skew is not sufficiently corrected.

For example, in the case of using rod-shaped rollers having different velocities on the right and on the left, instead of the transport rollers 302 and 304, the contact area with respect to the sheet 10 from the transport direction to the direction perpendicular to the transport direction is large, so that wrinkling is likely to occur.

It is obvious that such inconveniences and problems are overcome by using the above-described embodiments.

According to the sheet transport device, sheet transport control method, and printer disclosed herein, any one of the following advantages may be obtained.

(1) In the case of performing skew correction while transporting a sheet, the intervals of a plurality of transport members disposed on the right and on the left are varied. Accordingly, a transport load applied to the sheet is distributed and the occurrence of wrinkling may be suppressed.

(2) A plurality of rollers are disposed at different intervals from the upstream side toward the downstream side in a transport direction, and a large skew correction section is obtained. Accordingly, the rotation velocities of the individual transport members may be suppressed, skew correction may be appropriately performed, and the occurrence of wrinkling may be suppressed.

(3) A plurality of transport members having a small contact area are disposed at different intervals. Accordingly, a contact load applied to a sheet may be suppressed.

(4) Skew correction is performed on a sheet in a proper orientation. Accordingly, a printing process may be performed on the sheet at a proper position.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present invention has(have) been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 

1. A sheet transport device comprising: a detecting unit configured to detect skew with respect to a transport direction of a sheet that is supplied; a transport unit configured to transport the sheet using a plurality of transport members disposed on the right and on the left at different intervals from an upstream side toward a downstream side in the transport direction; and a control unit configured to cause rotation velocities of transport members on the right among the plurality of transport members to be different from rotation velocities of transport members on the left among the plurality of transport members in accordance with the skew of the sheet detected by the detecting unit.
 2. The sheet transport device according to claim 1, wherein the detecting unit includes a plurality of sensors disposed in a direction perpendicular to the transport direction, and determines whether or not detection timings of detecting the sheet by the plurality of sensors are the same, and wherein, when the detection timings are not the same, the control unit executes either or both of decreasing the rotation velocities of the transport members on the side of a sensor that detects the sheet first among the plurality of sensors, and increasing the rotation velocities of the transport members on the side of a sensor that detects the sheet later among the plurality of sensors.
 3. The sheet transport device according to claim 1, further comprising: a measuring unit configured to measure a detection time difference in the detecting unit, the detection time difference being caused by skew of the sheet that is transported, wherein the control unit calculates at least one of a skew distance and a skew angle on the basis of the rotation velocities and the detection time difference measured by the measuring unit, and determines a difference in rotation velocity between the transport members on the right and the transport members on the left and a transport period on the basis of one of the skew distance and the skew angle.
 4. The sheet transport device according to claim 1, wherein each of the plurality of transport members is constituted by a roller member having a reduced contact area that contacts the sheet.
 5. The sheet transport device according to claim 1, wherein the plurality of transport members of the transport unit are disposed in a V-like shape from the upstream side toward the downstream side in the transport direction.
 6. The sheet transport device according to claim 1, wherein the control unit controls the plurality of transport members so that the transport members on the right operate simultaneously and the transport members on the left operate simultaneously with respect to the transport direction.
 7. The sheet transport device according to claim 1, wherein the transport unit includes a plurality of driving motors for rotating the plurality of transport members, and wherein the control unit performs rotation control of each of the plurality of driving motors in accordance with the detected skew of the sheet.
 8. The sheet transport device according to claim 1, wherein the control unit minimizes a difference in rotation velocity between the transport members on the right and the transport members on the left on the basis of the detected skew.
 9. The sheet transport device according to claim 2, wherein the plurality of sensors include a light emitting unit configured to emit light to a measurement point, and a light receiving unit configured to receive the light emitted by the light emitting unit, and wherein, when the light emitted to the light receiving unit is cut off, the control unit determines that the sheet is detected.
 10. The sheet transport device according to claim 1, further comprising: a skew monitoring unit configured to monitor skew of the sheet that has passed the transport unit, wherein, when the skew monitoring unit detects the skew, the transport unit returns the sheet to a transport start position.
 11. A sheet transport control method comprising: detecting skew with respect to a transport direction of a sheet that is supplied; and performing control by causing rotation velocities of transport members on the right among a plurality of transport members to be different from rotation velocities of transport members on the left among the plurality of transport members in accordance with the detected skew of the sheet, the plurality of transport members being disposed on the right and on the left at different intervals from an upstream side toward a downstream side in the transport direction.
 12. The sheet transport control method according to claim 11, further comprising: determining whether or not detection timings of detecting the sheet by a plurality of sensors are the same, the plurality of sensors being disposed in a direction perpendicular to the transport direction; and when the detection timings are not the same, executing either or both of decreasing the rotation velocities of the transport members on the side of a sensor that detects the sheet first among the plurality of sensors, and increasing the rotation velocities of the transport members on the side of a sensor that detects the sheet later among the plurality of sensors.
 13. The sheet transport control method according to claim 11, further comprising: measuring, with a measuring unit, a detection time difference caused by skew of the sheet that is transported; calculating at least one of a skew distance and a skew angle on the basis of the rotation velocities and the detection time difference; and determining a difference in rotation velocity between the transport members on the right and the transport members on the left and a transport period on the basis of one of the skew distance and the skew angle.
 14. The sheet transport control method according to claim 11, further comprising: monitoring skew of the sheet that has been transported; and when skew is detected in the sheet that has been transported, returning the sheet to a transport start position.
 15. A printer comprising: a detecting unit configured to detect skew with respect to a transport direction of a sheet that is taken from a feeding unit; a transport unit configured to transport the sheet using a plurality of transport members disposed on the right and on the left at different intervals from an upstream side toward a downstream side in the transport direction; and a control unit configured to cause rotation velocities of transport members on the right among the plurality of transport members to be different from rotation velocities of transport members on the left among the plurality of transport members in accordance with the skew of the sheet detected by the detecting unit.
 16. The printer according to claim 15, wherein the detecting unit includes a plurality of sensors disposed in a direction perpendicular to the transport direction, and determines whether or not detection timings of detecting the sheet by the plurality of sensors are the same, and wherein, when the detection timings are not the same, the control unit executes either or both of decreasing the rotation velocities of the transport members on the side of a sensor that detects the sheet first among the plurality of sensors, and increasing the rotation velocities of the transport members on the side of a sensor that detects the sheet later among the plurality of sensors.
 17. The printer according to claim 15, further comprising: a measuring unit configured to measure a detection time difference in the detecting unit, the detection time difference being caused by skew of the sheet that is taken, wherein the control unit calculates at least one of a skew distance and a skew angle on the basis of the rotation velocities and the detection time difference measured by the measuring unit, and determines a difference in rotation velocity between the transport members on the right and the transport members on the left and a transport period on the basis of one of the skew distance and the skew angle.
 18. The printer according to claim 15, wherein the plurality of transport members of the transport unit are disposed in a V-like shape from the upstream side toward the downstream side in the transport direction.
 19. The printer according to claim 15, wherein the control unit includes a rotation velocity setting table in which minimized differences in rotation velocity between the transport members on the right and the transport members on the left are set on the basis of the detected skew.
 20. The printer according to claim 15, further comprising: a skew monitoring unit configured to monitor skew of the sheet that has passed the transport unit, wherein, when the skew monitoring unit detects the skew, the transport unit returns the sheet to a transport start position. 